1. Field of the Invention
The present invention relates in general to communication systems and in particular to methods and systems for transferring operations from a local inservice routing recommendation set of NPs (Network Processors), which recommendation set is connected to a plurality of NEs (network element) switches, to a geographically remote emergency routing recommendation set of NPs and re-establishing operations with that same plurality of NEs.
2. Description of the Related Art
A long distance telephone system comprises a plurality of high capacity signal routing switches, commonly designated as NEs (network elements), situated throughout the country and interconnected by high speed transmission lines. A telephone call from New York city to Los Angeles may take any of many paths across country through any of a plurality of NEs: When an NE, or a set of lines interconnecting a pair of NEs, becomes overloaded with traffic, some incoming calls may be blocked resulting in a busy signal. A new attempt to place an identical call may use a different set of NEs with the result that the call gets to its desired destination.
The apparatus that may cause calls to be routed through different NEs at different times is appropriately designated, in the telephony communication art, "a Routing Controller". When such a routing controller operates to make routing recommendations in substantially real time in accordance with information received a fraction of a minute previously, the process is termed DCR (Dynamically Controlled Routing). For reliability, there is usually an active NP or CPU (Control Processor Unit) and a standby or backup NP or CPU at a control site. The backup NP is typically ready to takeover the functions of the active NP. This action is transparent to the users of the telephone customers having communications through the NEs.
A routing controller receives reports from each of the NEs to which it is connected, assimilates the information related to the percentage of fully loaded capacity of each of the NEs, the number of idle trunks between NEs etc. and transmits recommendations, to each of the connected NEs, as to which NEs should be used, where possible, for future calls that may overflow from that calls direct route. Each NE has internally a set of rules that is used by an individual NE for following or ignoring the received recommendations.
The system described above has operated for many years with a high level of operability. If however, a major disaster occurs which destroys the site of the routing controllers or if there is a major power failure in the area of the routing controllers, it becomes desirable to have a geographically remote set of routing controllers ready to take over the functions of supplying the NEs with routing recommendations upon short notice.
A prior art ERS (Emergency Restoration System) has been used where a geographically remote set of backup NPs can be put into service to form the functions of active and standby routing controllers. This system included a plurality of command terminals, designated as UPs (User Positions), connected to the local and remote set of NPs through the use of a communication network. The prior art system used a synchronous method of gathering information from associated NEs, required updating the NPs with the latest configuration information and further required rebooting before even attempting to communicate with each of the NEs in the system and the UPs. Even where everything operated under optimum conditions, a switchover from a local to a remote set of routing controllers required approximately 30 minutes. Over a time period of 30 minutes, the loading conditions of each of the NEs in a large network of routing controllers such as occurs in the USA can change drastically. Such changes may cause many telephone calls may be blocked due to less than optimal routing of calls when the NEs are not receiving routing recommendations from a routing controller on a dynamic basis.
More information on the basic functions of routing controllers may be obtained from a U.S. Pat. No. 4,282,852 issued Aug. 18, 1981 to Szybicki et al. and assigned to Northern Telecom Limited.